[R] To calculate the month number between 2 dates

[Achim Zeileis]

On Fri, 7 Nov 2014, Arnaud Michel wrote:

> Hello
> Can one calculate the month number between two dates
> D1 <- "01/01/2007"  and D2 <- "01/04/2009" ?
> Thank you

One way is through zoo's yearmon class:

R> library("zoo")
R> D1 <- as.yearmon("01/01/2007", format = "%d/%m/%Y")
R> D2 <- as.yearmon("01/04/2009", format = "%d/%m/%Y")
R> D2 - D1
[1] 2.25
R> 12 * (D2 - D1)
[1] 27

Other solutions could go through base R's POSIXlt class, see strptime() 
and difftime().

hth,
Z

>
> -- 
> Michel ARNAUD
> Cirad
>
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